FIG. 1 diagrammatically illustrates the typical configuration of the output stage of a low dropout voltage regulator, which employs a common emitter-configured transistor in the output stage and thus allows the output-input voltage differential to be minimized at V.sub.CESAT (typically on the order of 0.5 volts). Specifically, the output stage is comprised of a common emitter-configured transistor 10, the emitter 11 of which is coupled to an input voltage terminal 20, to which an input voltage V.sub.in is applied. It's collector 13 is coupled to an output voltage terminal 30 from which a regulated output voltage V.sub.out is to be produced, and its base 12 is coupled to the output of an error amplifier 40. A first (non-inverting) input 41 of error amplifier 40 is coupled to output terminal 30 and is compared with a reference voltage 50 that is applied to a second (inverting) input 42 of amplifier 40. Error amplifier 40 serves to provide a feedback base drive to transistor 10 and thereby regulates the output voltage at output terminal 30.
As schematically illustrated in FIG. 1, the load 60 to which regulated voltage output terminal 30 is coupled is typically in the form of a (parallel) resistor-capacitor circuit, shown as having a resistor 61 and a capacitor 62 coupled between terminal 30 and a reference node (e.g. ground). Analysis of the transistor function of the circuit configuration of FIG. 1 reveals that the dominant pole is normally that of the RG load 60. With a typical value of resistor 61 on the order of 5 ohms and that of capacitor 62 on the order of 22 .mu.F, the resulting pole occurs at approximately 1 KHz, which is sufficently low to effectively assure closed loop stability of the system. However, as load parameters are substantially reduced, the location of the dominant pole is subject to a dramatic increase in frequency, which can result in a modification of the transfer function that the circuit goes into oscillation.
More particularly, the emphasis on increase in component integration density of microelectronic circuits has led to replacement of distributed power supply components by a single high power device that must be capable of meeting high output current (low output resistance) requirements. This significant (e.g. an order of magnitude) reduction in output resistance R.sub.L must be offset by a corresponding increase in load capacitance C.sub.L in order to maintain circuit stability. However, because of size constraints, the incorporation of a large valued capacitor is not practically feasible. Moreover, it may even be the case that the load capacitance is also reduced, thereby forcing the RC load pole to a frequency several orders of magnitude greater than the 1 KHz value, so that over a substantial portion of the operational frequency range, error amplifier 40 provides positive feedback, thus driving the output stage into oscillation.